Liquid chromatography (LC) is a well-known technique for separating the constituent elements in a given sample. In a conventional LC system, a liquid solvent (referred to as the “mobile phase”) is introduced from a reservoir and is pumped through the LC system. The mobile phase exits the pump under pressure. The mobile phase then travels via tubing to a sample injection valve. As the name suggests, the sample injection valve allows an operator to inject a sample into the LC system, where the sample will be carried along with the mobile phase.
In a conventional LC system, the sample and mobile phase pass through one or more filters and often a guard column before coming to the column. A typical column usually consists of a piece of steel tubing which has been packed with a “packing” material. The “packing” consists of the particulate material “packed” inside the column. It usually consists of silica- or polymer-based particles, which are often chemically bonded with a chemical functionality. The packing material is also known as the stationary phase. One of the fundamental principles of separation is the mobile phase continuously passing through the stationary phase. When the sample is carried through the column (along with the mobile phase), the various components (solutes) in the sample migrate through the packing within the column at different rates (i.e., there is differential migration of the solutes). In other words, the various components in a sample will move through the column at different rates. Because of the different rates of movement, the components gradually separate as they move through the column. Differential migration is affected by factors such as the composition of the mobile phase, the composition of the stationary phase (i.e., the material with which the column is “packed”), and the temperature at which the separation takes place. Thus, such factors will influence the separation of the sample's various components.
Once the sample (with its components now separated) leaves the column, it flows with the mobile phase past a detector. The detector detects the presence of specific molecules or compounds. Two general types of detectors are used in LC applications. One type measures a change in some overall physical property of the mobile phase and the sample (such as their refractive index). The other type measures only some property of the sample (such as the absorption of ultraviolet radiation). In essence, a typical detector in a LC system can measure and provide an output in terms of mass per unit of volume (such as grams per milliliter) or mass per unit of time (such as grams per second) of the sample's components. From such an output signal, a “chromatogram” can be provided; the chromatogram can then be used by an operator to determine the chemical components present in the sample.
In addition to the above components, a LC system will often include filters, check valves, a guard column, or the like in order to prevent contamination of the sample or damage to the LC system. For example, an inlet solvent filter may be used to filter out particles from the solvent (or mobile phase) before it reaches the pump. A guard column is often placed before the analytical or preparative column; i.e., the primary column. The purpose of such a guard column is to “guard” the primary column by absorbing unwanted sample components that might otherwise bind irreversibly to the analytical or preparative column.
In practice, various components in an LC system may be connected by an operator to perform a given task. For example, an operator will select an appropriate mobile phase and column, then connect a supply of the selected mobile phase and a selected column to the LC system before operation. In order to be suitable for high performance liquid chromatography (HPLC) applications, each connection must be able to withstand the typical operating pressures of the HPLC system. If the connection is too weak, it may leak. A leakage will definitely result in an unsuccessful or inaccurate analysis, such as inconsistent results or a total loss of the sample to be analyzed. Because the types of solvents that are sometimes used as the mobile phase are often toxic and because it is often expensive to obtain and/or prepare many samples for use, any such connection failure is a serious concern.
It is fairly common for an operator to disconnect a column (or other component) from a LC system and then connect a different column (or other component) in its place after one test has finished and before the next begins. Given the importance of leak-proof connections, especially in HPLC applications, the operator must take time to be sure the connection is sufficient. Replacing a column (or other component) may occur several times in a day. Moreover, the time involved in disconnecting and then connecting a column (or other component) is unproductive because the LC system is not in use and the operator is engaged in plumbing the system instead of preparing samples or other more productive activities. Hence, the replacement of a column in a conventional LC system involves a great deal of wasted time and inefficiencies.
Given concerns about the need for leak-free connections, conventional connections have been made with stainless steel tubing and stainless steel end fittings. More recently, however, it has been realized that the use of stainless steel components in a LC system have potential drawbacks in situations involving biological samples. For example, the components in a sample may attach themselves to the wall of stainless steel tubing. This presents problems because the detector's measurements (and thus the chromatogram) of a given sample may not accurately reflect the sample if some of the sample's components or ions remain in the tubing, and do not pass the detector. Perhaps of even greater concern, however, is the fact that ions from the stainless steel tubing may detach from the tubing and flow past the detector, thus leading to potentially erroneous results. Additionally, ions can easily bind to biological compounds of interest, resulting in changes to the molecules that affect their retention time in the column. Hence, there is a need for “biocompatible” connections through the use of a material that is chemically inert with respect to such “biological” samples and the mobile phase used with such samples so that ions will not be released by the tubing and thus contaminate the sample.
Multiport selector/injector valves are well known and have been used in a variety of industrial processes, such as liquid chromatography and mass spectrometry. For example, selection valves are commonly used in liquid chromatography and other analytical methods to direct fluid flow along alternate paths. Such valves are also used to terminate fluid withdrawal from one source and select another source of fluid, for example, such as when a variety of streams in an industrial process is selectively sampled for analysis.
Injector/selector valves are often used in high pressure liquid chromatography (HPLC) or gas chromatography (GC). U.S. Pat. No. 4,242,909 (Gundelfinger '909), which is hereby fully incorporated by reference, describes sample injection apparatus for withdrawing liquid samples from vials and injecting them into a chromatographic column or other analyzing device. The apparatus is said to minimize wastage, cross contamination, and dilution of the samples, and to be capable of automation with a minimum of complexity. Injector/selector valves are particularly useful in chromatographic applications since a substantial amount of time and effort is required to set up a particular HPLC or GC system, which may often utilize multiple columns and/or multiple detection systems. Multiport selection valves permit the operator of the chromatograph to redirect flows such that particular samples are selected for injection into a particular column, or alternatively, to direct the output from a particular column to one or more different detectors.
As mentioned above, multiport selection valves have been known for some time, including those which utilize a cylindrical rotor and stator combination. In some of these valves, the stator holds the fluid tubes in fixed relation to each other and presents the tube ends to a rotor face which may contain a grooved surface. By varying the angle of the rotor, the tubes are selectively brought into fluid communication. One type of injector/selector valve using a rotor/stator combination is the Type 50 rotary valve from Rheodyne, Incorporated. The Type 50 valves are said to operate by rotation of a flat rotor against a flat stator (see “Operating Instructions for Type 50 Teflon Rotary Valves,” Rheodyne, Incorporated, printed in U.S.A. April 1994). Another rotor/stator selector valve is shown in U.S. Pat. No. 5,193,581 (Shiroto, et al.), which is hereby fully incorporated by reference. The valve is said to comprise, among other things, a stator plate having a plurality of outlet holes extending through the stator plate and arranged in a circle concentric with a valve casing, and a rotor having a U-shaped passage formed in the rotor. The rotor is said to be rotated through a desired angle so that an inlet hole can be in fluid communication with selected ones of the outlet holes through the U-shaped passage of the rotor.
U.S. Pat. No. 5,419,419 (Macpherson) describes a rotary selector valve that is used in connection with an automatic transmission in an automobile. A motor is said to index a shear plate of the selector valve to predetermined positions for shifting the transmission. A series of working lines as shown in FIG. 6 are maintained in a closed spatial relationship with the casing.
U.S. Pat. No. 3,494,175 (Cusick, et al.) discloses a valve having a plurality of capillaries which are held in spaced relationship within a manifold plate member. U.S. Pat. No. 3,752,167 (Makabe) discloses a fluid switching device including a plurality of capillaries that are held within threaded holes by couplings. A rotary member allows fluid communication between the tubes. U.S. Pat. No. 3,868,970 (Ayers, et al.) discloses a multipositional selector valve said to be adapted with a means for attaching a plurality of chromatographic columns to the valve, such that the flow can be directed into any of the columns. U.S. Pat. No. 4,705,627 (Miwa, et al.) discloses a rotary valve said to consist of two stator discs and a rotor disposed between the two stator discs. Each time the rotor is turned intermittently it is said, different passages are formed through which the fluid in the valve runs. U.S. Pat. No. 4,722,830 (Urie, et al.) discloses multiport valves. The multiport valves are said to be used in extracting fluid samples from sample loops connected with various process streams.
In many applications using selector/injector valves to direct fluid flows, and in particular in liquid and gas chromatography, the volume of fluids is small. This is particularly true when liquid or gas chromatography is being used as an analytical method as opposed to a preparative method. Such methods often use capillary columns and are generally referred to as capillary chromatography. In capillary chromatography, both gas phase and liquid phase, it is often desired to minimize the volume of the fluid flowpath (e.g., length and/or size of the fluid pathways) of the valve. One reason for this is that a valve having a larger volume for the fluid flowpath will contain a relatively larger volume of liquid, and when a sample is injected into the valve the sample will be diluted, decreasing the resolution and sensitivity of the analytical method, and may result in a dead volume being introduced into the fluid pathway.
Micro-fluidic analytical processes also involve small sample sizes. As used herein, sample volumes considered to involve micro-fluidic techniques can range from as low as volumes of only several picoliters or so, up to volumes of several milliliters or so, whereas more traditional LC techniques, for example, historically often involved samples of about one microliter to about 100 milliliters in volume. Thus, the micro-fluidic techniques described herein involve volumes one or more orders of magnitude smaller in size than traditional LC techniques. Micro-fluidic techniques can also be expressed as those involving fluid flow rates of about 0.5 ml/minute or less.
Most conventional HPLC systems include pumps which can generate relatively high pressures of up to around 5,000 psi to 9,000 psi or so. In many situations, an operator can obtain successful results by operating a LC system at “low” pressures of anywhere from just a few psi or so up to 1,000 psi or so. More often than not, however, an operator will find it desirable to operate a LC system at relatively “higher” pressures of over 1,000 psi.
Another, relatively newer liquid chromatography form is Ultra High Performance Liquid Chromatography (UHPLC) in which system pressure extends upward to about 1400 bar or 20,000 psi or so, or even more. In order to achieve greater chromatographic resolution and higher sample throughput, the particle size of the stationary phase has become extremely small. A stationary phase particle as small as 1 micron is common; the resulting high column packing density leads to substantially increased system pressure at the head of the column. Both HPLC and UHPLC are examples of analytical instrumentation that utilize fluid transfer at elevated pressures. For example, in U.S. Patent Publication No. 2007/0283746 A1, published on Dec. 13, 2007 and titled “Sample Injector System for Liquid Chromatography,” an injection system is described for use with UHPLC applications, which are said to involve pressures in the range from 20,000 psi to 120,000 psi. In U.S. Pat. No. 7,311,502, issued on Dec. 25, 2007 to Gerhardt, et al., and titled “Method for Using a Hydraulic Amplifier Pump in Ultrahigh Pressure Liquid Chromatography,” the use of a hydraulic amplifier is described for use in UHPLC systems involving pressures in excess of 25,000 psi. In U.S. Patent Publication No. 2005/0269264 A1, published on Dec. 8, 2005 and titled “Chromatography System with Gradient Storage and Method for Operating the Same,” a system for performing UHPLC is disclosed, with UHPLC described as involving pressures above 5,000 psi (and up to 60,000 psi). Applicants hereby incorporate by reference as if fully set forth herein U.S. Pat. No. 7,311,502 and US Patent Publications Nos. 2007/0283746 A1 and 2005/0269264 A1.
As noted, liquid chromatography (as well as other analytical) systems, including HPLC or UHPLC systems, typically include several components. For example, such a system may include a pump; an injection valve or autosampler for injecting the analyte; a precolumn filter to remove particulate matter in the analyte solution that might clog the column; a packed bed to retain irreversibly adsorbed chemical material; the HPLC column itself; and a detector that analyzes the carrier fluid as it leaves the column. These various components may typically be connected by a miniature fluid conduit, or tubing, such as metallic or polymeric tubing, usually having an internal diameter of 0.001 to 0.040 inch.
All of these various components and lengths of tubing are typically interconnected by threaded fittings. Fittings for connecting various LC system components and lengths of tubing are disclosed in prior patents, for example, U.S. Pat. Nos. 5,525,303; 5,730,943; and 6,095,572, the disclosures of which are herein all incorporated by reference as if fully set forth herein. Often, a first internally threaded fitting seals to a first component with a ferrule or similar sealing device. The first fitting is threadedly connected through multiple turns by hand or by use of a wrench or wrenches to a second fitting having a corresponding external fitting, which is in turn sealed to a second component by a ferrule or other seal. Disconnecting these fittings for component replacement, maintenance, or reconfiguration often requires the use of a wrench or wrenches to unthread the fittings. Although a wrench or wrenches may be used, other tools such as pliers or other gripping and holding tools are sometimes used. It will be understood by those skilled in the art that, as used herein, the term “LC system” is intended in its broad sense to include all apparatus and components in a system used in connection with liquid chromatography, whether made of only a few simple components or made of numerous, sophisticated components which are computer controlled or the like. Those skilled in the art will also appreciate that an LC system is one type of an analytical instrument (AI) system. For example, gas chromatography is similar in many respects to liquid chromatography, but obviously involves a volatile sample to be analyzed, and uses a gas as a mobile phase. Such analytical instrument systems include high performance or high pressure liquid chromatography systems, an ultra high performance or ultra high pressure liquid chromatography system, a mass spectrometry system, a microflow chromatography system, a nanoflow chromatography system, a nano-scale chromatography system, a capillary electrophoresis system, a reverse-phase gradient chromatography system, or a combination thereof. Although the following discussion focuses on liquid chromatography, those skilled in the art will appreciate that much of what is said also has application to other types of AI systems and methods.
Increasing pressure requirements in liquid chromatography have necessitated the use of high pressure fluidic components. For many applications regular stainless steel tubing can be used to withstand the high pressure. However, for some types of analyses (e.g., biological testing and metal/ion analysis), stainless steel or other metals are not desired in the fluid path as the metal could interfere with the testing. Additionally, there are some fields of use (e.g., nano-scale or nano-volume analysis), that require very small inside diameters to accommodate the extremely low volumes required by these applications. Such small inside diameters are typically not available in stainless steel or other high pressure tubing.
In high-performance liquid chromatography (HPLC), ultra high-performance liquid chromatography (UHPLC), and other high-pressure analytic chemistry applications, various system components and their fluidic connections must be able to withstand pressures of 15,000 to 20,000 psi or so. The types of fluidic connection systems between the tubes that carry fluids and the ports that receive fluids in these high-pressure applications are limited. Many fluidic connection systems rely on cone-shaped, threaded, or welded fittings to attach a tube to a receiving port. These types of connections sometimes may have drawbacks, however. For example, the size of cone-shaped fittings and threaded fittings are dependent on the type and size of any given port, which makes quickly interchanging a tube fitted with a particular cone or threaded fitting between various ports difficult. Other compression-based fittings have been employed to address this problem. Such fittings often employ a ferrule or a lock ring to help secure one end of a tube to a receiving port. However, ferrules and lock rings can become deformed after multiple uses (e.g., by connecting, disconnecting, and reconnecting to various ports). This is especially true in high-pressure applications, where a fluid-tight seal is essential, and where a ferrule or lock ring may be more likely to become deformed in creating such a seal.
For example, published U.S. Patent Application No. 2013/0043677, titled “Tube and Pipe End Cartridge Seal,” published on Feb. 21, 2013, describes a tube and pipe end cartridge seal for use at high pressures, which relies on a fitting body (including ferrule fittings) to effectuate a seal with the axial end of a tube. Moreover, a dimple is forged on the annular end of the tube face to further effectuate the seal. Likewise, U.S. Pat. No. 6,056,331, titled “Zero Dead Volume Tube to Surface Seal,” issued to Bennett et al. on May 2, 2000, describes an apparatus for connecting a tube to a surface using a body, a ferrule, and a threaded fitting. Although Bennett et al. discloses a type of tube face-sealing apparatus, the apparatus of Bennet et al. relies on a threaded fitting and a ferrule. Similarly, published U.S. Patent Application No. 2012/0061955, titled “Plug Unite and Connection System for Connecting Capillary Tubes, Especially for High-Performance Liquid Chromatography,” published on Mar. 15, 2012, discloses a plug unit connection system for capillary tubes, wherein a seal is provided at the interface between a capillary tube and a bushing unit, instead of at the location of a ferrule or conical fitting. However, U.S. Patent Application No. 2012/0061955 relies on the use of a pressure piece similar to a ferrule to ensure that enough axial force can be generated to obtain a seal at the tube face.
Connection assemblies which attempt to effectuate a seal for high-pressure applications can require a significant amount of torque to effectuate a fluid-tight seal, making the creation of such seals difficult without the use of additional tools and increasing the risk of damage to the fitting assembly or its components due to overtightening. Moreover, experience suggests that many users do not like to use various tools to connect or disconnect tubing from components such as those in various AI systems. It is believed that users often apply different amounts of torque to connect or disconnect tubing and the components in such systems, thus resulting in potential problems caused by over-tightening or under-tightening (e.g., leakage or loss of sealing when the fluid is under pressure).
One example of a flat-bottomed or face-sealing connection assembly is provided by U.S. Pat. No. 8,696,038, titled “Flat Bottom Fitting Assembly” and issued on Apr. 15, 2014 to Nienhuis. Nienhuis teaches a type of flat bottom assembly which includes a flat-sided ferrule, and wherein the assembly including the ferrule and the tube can be pressed against a flat bottom port. Another example of a flat-bottomed or face-sealing connection assembly is provided by published U.S. Patent Application No. 2012/0024411, titled “Biocompatible Tubing for Liquid Chromatography Systems,” which was published on Feb. 2, 2012 and was filed on behalf of Hahn et al. The Hahn et al. published patent application describes tubing having an inner layer and an outer layer, and in which the inner layer can be biocompatible material such as polyetheretherketone (PEEK) and the outer layer may be a different material, and in which an end of the tubing may be flared or otherwise adapted to have a larger outer diameter than other portions of the tubing. The current state of the art for high pressure connections in both HPLC and UHPLC is to utilize coned ports along with some form of ferrule and nut combination with tubing. The nut translates rotational torque into axial load that is translated to the ferrule. The load causes the ferrule to deform/deflect and grip the tubing, creating a seal. The tube is typically forced into the bottom of the coned port, but there is not currently a mechanism to ensure there is not a gap or space at the port bottom.
The space at the bottom of the port is a concern for those performing liquid chromatography experiments due to the potential to negatively influence the results with carry over and band broadening. Carry over is just as it sounds, analyte from one test is carried over to the next. Carry over can produce very unstable results for obvious reasons. Band broadening is when the peaks identifying a substance become less symmetric and make identification more difficult when peaks of different molecules have similar retention times.
One issue with conventional ferrules used with coned ports is that the torque required to deform/deflect is typically above finger tight levels in order to achieve UHPLC pressures (e.g., above 12,000 psi or so). It is desirable to remove tools from the lab by making them unnecessary for making and breaking fluidic connections and it is advantageous to have fittings that can be connected simply with the fingers rather than tools.
European Patent No. EP 2564104 describes a sealing system for use at high pressure. End-face seals minimize the sealing radius and therefore allow various fittings—including known ferrule fittings—to be used in high-pressure systems. End-face seals at such high pressure may require smooth surfaces, however. In order to reduce cost, an end-face preparation tool may be required to forge a dimple into the end face to mechanically deform and smooth the surface.
U.S. Pat. No. 6,056,331 describes an apparatus that is composed of three components, a body, a ferrule, and a threaded fitting. The ferrule is compressed onto a tube and a seal is formed between the tube and a device retained in the body by threading the fitting into the body which provides pressure that seals the face of the ferrule to a mating surface on the device. This seal may be used at elevated temperatures, depending on the materials used. This fitting was developed for use with micro-machined silicon wafers used in capillary gas chromatography.
In many conventional valves, such as rotary shear valves, a stator member at one end has two or more ports to receive tubing which can be removably attached to provide fluid connections to the valve. Such a stator member typically serves as least two functions: it provides a planar stator face which mates with a rotor seal, and also provides fluid channels or pathways between the ports and the stator face. In typical such valves, the stator member is a single piece and is often designed so that the ports to receive the tubing are oriented at angles with respect to the longitudinal axis of the stator member and the valve generally. This approach is generally due to the need to provide several ports on the end surface of the stator member, as well as several screws or nuts to secure the stator member to the valve body, and the limited size of the stator member and the resulting limited space available for the ports, as well as the need to allow enough space for an operator to connect and disconnect tubing from the ports of the stator member. An example of a valve with such a single-piece stator is described and shown in U.S. Pat. No. 8,905,075 B2, issued on Dec. 9, 2014, to Tower, and entitled “Rotary Shear Valve Assembly with Hard-on-Hard Seal Surfaces,” which is hereby incorporated by reference as if fully set forth herein.
While this configuration has worked in the past, and still works for many applications, it also typically requires that the fluid passageways between the ends of the tubing and the stator face are longer and therefore have a greater volume than may be desired. Those skilled in the art will appreciate that the volumes in valves used for analytical science applications generally require very precise control over the volumes of the fluid passageways, and the use of smaller and smaller sample sizes means that the precise control of such volumes can become important. In addition, stator members of this type are often made of metal, such as stainless steel, and the manufacturing and machining of such stator members can be costly and time consuming. The use of angled ports tends to require that the stator member be larger in size, and this also tends to increase the costs of such stator members. In addition to these issues, the alignment of the fluid flowpaths of the components once assembled can be problematic with such conventional stator members. It will be appreciated that the tubing will have an inner diameter through which the fluid flows, and the ports of the stator member will likewise have openings at the bottom of the ports, with those openings providing fluid passageways. If the stator member surface has been lapped during manufacturing, which is often the case, then the openings of the ports may shift in shape, size or location, thereby causing potential difficulties in the alignment of the openings; the alignment of the openings is usually desired in order to prevent turbulent fluid flow.
U.S. Pat. Nos. 3,494,175, 3,752,167, 3,868,970, 4,242,909, 4,705,627, 4,722,830, 5,193,581, 5,419,419, 5,525,303, 5,730,943, 6,056,331, 6,095,572, 7,311,502, 7,811,452, 8,071,052, 8,696,038, European Patent No. EP2564104, and published U.S. Patent Application Nos. 2005/0269264, 2007/0283746, 2009/0321356, 2010/0171055, 2012/0024411, 2012/0061955, 2013/0043677, and 2016/0116088 are hereby incorporated by reference as if fully set forth herein.